Ubuntu Manpage: morphy - discussion of WordNet's morphological processing

NAME

       morphy - discussion of WordNet's morphological processing

DESCRIPTION

Although only base forms of words are usually stored in WordNet, searches may be done on inflected forms.
A set of morphology functions, Morphy, is applied to the search string to generate a form that is present
in WordNet.

Morphology in WordNet uses two types of processes to try to convert the string passed into one that can
be found in the WordNet database. There are lists of inflectional endings, based on syntactic category,
that can be detached from individual words in an attempt to find a form of the word that is in WordNet.
There are also exception list files, one for each syntactic category, in which a search for an inflected
form is done. Morphy tries to use these two processes in an intelligent manner to translate the string
passed to the base form found in WordNet. Morphy first checks for exceptions, then uses the rules of
detachment. The Morphy functions are not independent from WordNet. After each transformation, WordNet is
searched for the resulting string in the syntactic category specified.

The Morphy functions are passed a string and a syntactic category. A string is either a single word or a
collocation. Since some words, such as axes can have more than one base form (axe and axis), Morphy
works in the following manner. The first time that Morphy is called with a specific string, it returns a
base form. For each subsequent call to Morphy made with a NULL string argument, Morphy returns another
base form. Whenever Morphy cannot perform a transformation, whether on the first call for a word or
subsequent calls, NULL is returned. A transformation to a valid English string will return NULL if the
base form of the string is not in WordNet.

The morphological functions are found in the WordNet library. See morph(3WN) for information on using
these functions.

Rules of Detachment
The following table shows the rules of detachment used by Morphy. If a word ends with one of the
suffixes, it is stripped from the word and the corresponding ending is added. Then WordNet is searched
for the resulting string. No rules are applicable to adverbs.

│ │
POS │ Suffix │ Ending
─────┼────────┼────────
NOUN │ "s" │ ""
NOUN │ "ses" │ "s"
NOUN │ "xes" │ "x"
NOUN │ "zes" │ "z"
NOUN │ "ches" │ "ch"
NOUN │ "shes" │ "sh"
NOUN │ "men" │ "man"
NOUN │ "ies" │ "y"
VERB │ "s" │ ""
VERB │ "ies" │ "y"
VERB │ "es" │ "e"
VERB │ "es" │ ""
VERB │ "ed" │ "e"
VERB │ "ed" │ ""
VERB │ "ing" │ "e"
VERB │ "ing" │ ""
ADJ │ "er" │ ""
ADJ │ "est" │ ""
ADJ │ "er" │ "e"
ADJ │ "est" │ "e"

Exception Lists
There is one exception list file for each syntactic category. The exception lists contain the
morphological transformations for strings that are not regular and therefore cannot be processed in an
algorithmic manner. Each line of an exception list contains an inflected form of a word or collocation,
followed by one or more base forms. The list is kept in alphabetical order and a binary search is used
to find words in these lists. See wndb(5WN) for information on the format of the exception list files.

Single Words
In general, single words are relatively easy to process. Morphy first looks for the word in the
exception list. If it is found the first base form is returned. Subsequent calls with a NULL argument
return additional base forms, if present. A NULL is returned when there are no more base forms of the
word.

If the word is not found in the exception list corresponding to the syntactic category, an algorithmic
process using the rules of detachment looks for a matching suffix. If a matching suffix is found, a
corresponding ending is applied (sometimes this ending is a NULL string, so in effect the suffix is
removed from the word), and WordNet is consulted to see if the resulting word is found in the desired
part of speech.

Collocations
As opposed to single words, collocations can be quite difficult to transform into a base form that is
present in WordNet. In general, only base forms of words, even those comprising collocations, are stored
in WordNet, such as attorney general. Transforming the collocation attorneys general is then simply a
matter of finding the base forms of the individual words comprising the collocation. This usually works
for nouns, therefore non-conforming nouns, such as customs duty are presently entered in the noun
exception list.

Verb collocations that contain prepositions, such as ask for it, are more difficult. As with single
words, the exception list is searched first. If the collocation is not found, special code in Morphy
determines whether a verb collocation includes a preposition. If it does, a function is called to try to
find the base form in the following manner. It is assumed that the first word in the collocation is a
verb and that the last word is a noun. The algorithm then builds a search string with the base forms of
the verb and noun, leaving the remainder of the collocation (usually just the preposition, but more words
may be involved) in the middle. For example, passed asking for it, the database search would be
performed with ask for it, which is found in WordNet, and therefore returned from Morphy. If a verb
collocation does not contain a preposition, then the base form of each word in the collocation is found
and WordNet is searched for the resulting string.

Hyphenation
Hyphenation also presents special difficulties when searching WordNet. It is often a subjective decision
as to whether a word is hyphenated, joined as one word, or is a collocation of several words, and which
of the various forms are entered into WordNet. When Morphy breaks a string into "words", it looks for
both spaces and hyphens as delimiters. It also looks for periods in strings and removes them if an exact
match is not found. A search for an abbreviation like oct. return the synset for { October, Oct }. Not
every pattern of hyphenated and collocated string is searched for properly, so it may be advantageous to
specify several search strings if the results of a search attempt seem incomplete.

Special Processing for nouns ending with 'ful'
Morphy contains code that searches for nouns ending with ful and performs a transformation on the
substring preceeding it. It then appends 'ful' back onto the resulting string and returns it. For
example, if passed the nouns boxesful, it will return boxful.

BUGS

       Since many noun collocations contains prepositions, such as line of products,  an  algorithm  similar  to
       that  used  for  verbs  should  be  written  for  nouns.   In  the  present  scheme,  if Morphy is passed
       lines of products, the search string becomes line of product, which is not in WordNet

       Morphy will allow non-words to be converted to words, if they follow one of the  rules  described  above.
       For example, it will happily convert plantes to plants.

ENVIRONMENT VARIABLES (UNIX)

       WNHOME              Base directory for WordNet.  Default is /usr/local/WordNet-3.0.

       WNSEARCHDIR         Directory in which the WordNet database has been installed.  Default is WNHOME/dict.

REGISTRY (WINDOWS)

       HKEY_LOCAL_MACHINE\SOFTWARE\WordNet\3.0\WNHome
                           Base directory for WordNet.  Default is C:\Program Files\WordNet\3.0.

FILES